Cigarette smoke (CS) is a toxic mixture of reactive chemicals distributed between tar and gas phases. Many of these compounds are directly or indirectly destructive by generation of reactive oxygen species (ROS) or by depletion of sulfhydryl-containing antioxidants. As a result, irreversible oxidative stress-induced damage to cellular components of the lung epithelium by inhaled cigarette smoke may occur and has been linked to the pathogenesis of cardiovascular disorders and chronic obstructive pulmonary disease. CS-induced oxidative stress may also cause DNA damage and uncontrolled cell proliferation that could lead to lung cancer. Our overall objective is to characterize the toxic effects of electrophilic and/or redox-active conjugated ketones from different cigarette brands marketed as being modified for harm reduction. Conjugated ketones, such as unsaturated ?,?-aldehydes and quinones are of toxicological importance because they promote oxidative stress and eventually lead to cellular damage in the lung by covalently modifying cellular macromolecules. These highly reactive chemicals are detected in large but variable concentrations in cigarette combustion products. However, comparative emission data for combustible reduced risk tobacco products are rare and a comprehensive toxicity assessment outside of the tobacco industry is lacking. Our overarching hypothesis is that different types of cigarettes can be characterized by measuring the electrophilic and redox active constituents in CS gas- and tar-phase extracts and that the differential toxicity of these compounds will be reflected by different antioxidant responses in cell-free and cell-based bioassays. We will test our hypotheses with the following three aims: 1. Advance methods to generate, sample and quantify electrophilic gas-phase carbonyls and tar-phase quinones in cigarette smoke. 2. Assess the electrophilic and redox potential of gas phase carbonyls and tar phase quinones in cigarette smoke extracts derived from different types of cigarettes 3. Assess the differential effects of cigarette smoke components from modified tobacco products on the antioxidant defense mechanisms of cultivated primary small airway epithelial cells (SAECs) This will be among the first studies to compare electrophilic and pro-oxidative components in different CS fractions between cigarette types. Cutting-edge methods will be adapted to accurately quantify these components. The proposed study will provide new insights into the impact on antioxidant enzyme systems by electrophilic and redox-active compounds in both standard and so-called harm reduction cigarettes. The study is also expected to guide further research on the biological and clinical impacts of electrophilic carbonyls and quinones in cigarette smoke.